Polyvinylidene fluoride (PVDF) is a chemically resistant engineering plastic. The PVDF becomes increasingly brittle as its glass transition temperature is approached and loses impact resistance. Impact resistance is especially important for pipes, hoses and other melt-processed articles used in cold climates.
Copolymers of PVDF and perfluoroalkyl vinyl ether (PAVE) have been synthesized as curable elastomers (U.S. Pat. No. 3,136,745) showing good low-temperature properties when the PAVE content was between 17 and 75 mole percent. Terpolymers incorporating PAVE also showed good low temperature properties (U.S. Pat. No. 3,235,537).
The problem with the processes used to produce the PVDF/PAVE copolymers in the art is that they produce homogeneous copolymers with lower melting points, which can adversely effect the temperature usage range of the final articles. For Example the PVDF/perfluoromethylvinyl ether (PMVE) copolymers described in U.S. Pat. No. 6,630,271 of between 1.9 and 4.8 mole % PMVE have melting points of 134-153° C.
Heterogeneous copolymers of PVDF and hexafluoropropylene have been produced by a process in which the copolymer is introduced only in the latter stages of the polymerization. (U.S. Pat. No. 5,093,427).
It is desired to improve the impact resistance of PVDF by copolymerization with PAVE without any significant decrease in polymer melting point.
It has been found that heterogeneous copolymers of polyvinylidene fluoride with one or more perfluoroalkyl vinyl ethers have both excellent low temperature impact properties, and also maintain high melting temperatures.